Mesh bags are used to package various products, for instance, produce is often packaged in mesh bags to allow the produce to breath. Thermal sealable plastic mesh is often used to allow efficient application of thermal sealable print bands to the mesh for labelling and advertising. The mesh bags are preformed and filled either manually or semi-automatically. Thermal sealable plastic mesh is often used to allow efficient application of thermal sealable print bands to the mesh for labelling and advertising. The bottom cross seam of the preformed bags is normally sewn across the entire transverse length of the bag to provide sufficient bag strength. In the semiautomatic process, the preformed bag is secured to a filling mandril, the produce is manually put into the bag, and the top of the bag is hog-tied or crimped shut with a ring. This type of loading is labor-intensive and costly.
Automatic form, fill and seal machines are widely used in the packaging industry and significantly reduce packaging costs, especially labor costs associated with loading. Conventional automatic form, fill and seal machines contemporaneously form, fill and seal a bag from a heat sealable film continuously unwound from a roll. The process involves forming a tube from a layer of the heat sealable film unwound from the roll and heat sealing the longitudinal edges of the film together to form a back seam for the bag. The back seam is typically either a lap seal or a fin seal. The sealed tube is then pulled or driven downward for a distance equalling the length of the bag being formed. Transverse heat sealing jaws close to contemporaneously form the bottom cross seal for the bag and the top cross seal for the previous bag. The cross seal is cut and the previous bag falls into a bin or onto a conveyor, etc. At the same time, the open bag is filled. Automatic form, fill and seal machines are either gravity fed (e.g. vertical form, fill and seal machines) or mechanically fed (e.g. horizontal form, fill and seal machines).
Automatic form, fill and seal machines are efficient and cost effective when using many types of non-mesh films. However, bags produced from form, fill and seal machines using thermal sealable mesh have insufficient seam strength along the bottom and top fin seal for most practical uses. Therefore, to date, virtually all mesh bags are pre-formed with a sewn bottom cross seam.